Conventionally, a determination whether an in-focus is achieved or not is conducted based on a contrast of an image in an entire image area or in a specific area such as an auto-focus selection area. Specifically, it is determined that the in-focus is achieved as the contrast becomes higher and an out-of-focus occurs as the contrast becomes lower.
According to Patent Document 1, high frequency components in a specific area of an image are extracted and integrated. The document discloses that the integrated value is used as an evaluated value indicating a contrast in the specific area to determine whether an in-focus is achieved or not.
According to Patent Document 2, two high frequency components having different cutoff frequencies in a specific area of an image are respectively extracted. The document discloses that a focusing time taken for focusing on an in-focus position is shortened by appropriately changing a movement speed of an imaging lens of an imaging device in accordance with a displacement width from the in-focus position based on an evaluated value calculated from the two high frequency components.    Patent Document 1: Japanese Patent Publication No. 3840725    Patent Document 2: Japanese Unexamined Patent Application Publication No. Hei 10-221594